This invention relates generally to gas turbine engines and more particularly to exhaust duct liner attachment systems and methods. In gas turbine engines, it is necessary to protect exhaust ducts with an insulating shield in order to prevent heated core gases from damaging the exhaust ducts. Typically, exhaust ducts are made from titanium-based alloys and have temperature limits of approximately 300°-600° F. (˜148.9°-315.6° C.). Exhaust gases, however, reach much higher temperatures. It is, therefore, necessary to line exhaust ducts with a material that is capable of withstanding the peak temperatures of the core gases and that prevents the exhaust duct from reaching its temperature limitations. Exhaust duct liners are typically made from nickel-based alloys, which have temperature limits of approximately (˜371.1°-815.6° C.). In order to alleviate some of the heat from the exhaust gases imparted to the liner, cooling air is passed between the exhaust duct and liner. For example, bypass air is routed between the duct and liner in turbofan engines. Thus, the exhaust duct and liner are subjected to different pressure and temperature gradients, which results in differing deflections and expansions of each body.
In order to maintain the desired temperature and pressure profile along the exhaust duct and liner, it is desirable to maintain proper spacing between the exhaust duct and liner. The differing pressures, temperatures and functional requirements of the exhaust duct, however, produce three-dimensional forces between the duct and liner, which tend to shift the liner out of alignment during different operating conditions of the engine. Various liner hanger designs have been put forth to maintain proper alignment, such as described in U.S. Pat. No. 7,866,158 and U.S. Pat. App. Pub. No. 2009/0016880, which are assigned to United Technologies Corporation. In these designs, alternating upside-down and right-side-up U-shaped brackets on the liner and exhaust duct, respectively, are connected by a rod. These liner hanger designs typically rely on pressure from the bypass cooling air to maintain the brackets in tension. The brackets, however, are inefficient in reacting compressive loading between the duct and liner. There is, therefore, a need for an exhaust duct liner suspension system that permits the liner to shift within the duct, but that also reacts both radial compressive and radial tensile loads between the duct and liner.